1. BAN THE BOUNCEOne of the best investments you can make for your breasts is to buy a few quality sports bras. "High-impact exercise, like running and jumping rope, can contribute to premature sagging by stretching out the ligaments in your breasts," says Sabrena Merrill, Lawrence-Kansas-based personal trainer and spokeswoman for the American Council on Exercise. In fact, a woman's breast moves about three and a half inches while running, according to a study from the University of Portsmouth in England.

To stave off sag, look for sports bras with separate molded cups, which support breasts without squashing them, says Merrill. Two we love: CW-X Ultra Support bra ($74; zappos.com) and the Champion Shape T-back ($36; championusa.com). When trying on these undergarments, jump up and down several times in the fitting room; if your breasts move at all, search for another brand or smaller size. Ideally, you should replace your bras every six months, she says, since the elastic breaks down with wear.

2. EVEN OUT SKIN TONEEven out skin tone "As you age, you may begin to notice brown spots and fine lines on your chest, as well as thinning skin," says David Bank, a dermatologist in Mount Kisco, New York. A prescription retinoid cream like Renova can help plump up the skin, giving it a more youthful appearance. An in-office option: two to five treatments with the Fraxel lasel (about $500 a session), which sloughs off discoloration and forces your body to produce more collagen.

3. PUMP UP YOUR POSTUREYears of sitting at an office desk can take a toll on your body, overstretching and weakening your back and shoulder muscles. "As a result, a lot of women in this age group slouch forward, which makes their breasts look droopier," says Merrill. She recommends doing posture-enhancing exercises like the plank to strengthen your core and shoulder muscles. Other must-do moves: seated rows, lat pull-downs, and the yoga pose called the cobra.